Fuel injection pump with pneumatic damper



Nov. 9, 1965 C. A. TEICHERT FUEL INJECTION PUMP WITH PNEUMATIC DAMPER Filed April 22, 1963 Zl ii 55 Z 32 Z6 I -2; x; g2;

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16 {I I 5 J /7 INVENTOR. QvzmaAYe/crler/ BY United States Patent 3,216,359 FUEL INJECTKON PUMP WITH PNEUMATKC DAMEER Conrad A. Teiichert, Grand Rapids, Mich, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware I Filed Apr. 22, 1963, fier. No. 274,409 (Ilaims. (U. 103-41) This invention relates to fuel injection pumps, and particularly those of the so-called jerk type wherein the injection pressure developed by a spring opposed plunger during its pumping stroke is suddenly dissipated to end the injection by the plunger uncovering a bypass port in the side wall of the pumping chamber.

It has been found from experience that in some engine installations the plunger return spring surges at certain engine speeds, and that this surge is caused by the sudden pressure drop in the pump chamber at the end of the injection period. This sudden reduction of hydraulic pressure acting on the lower plunger area, being resisted by the spring-action of the rocker-lever and associated drive train components, excites the plunger spring to vibrate at its natural frequency. It has previously been proposed to prevent such spring surge by employing expansible fluid under pressure in opposition to the axial movement of the plunger on its pumping stroke, such fluid being subjected to compression in a chamber during the plunger fuel pumping stroke by a piston carried by the plunger. In such prior arrangement, the fluid is supplied from an external source via a supply connection on the pump. Notwithstanding proper sealing of the sliding surfaces and the use of a non-return valve at the supply connection, some loss of the fluid from the chamber necessarily ocours in operation, necessitating the chamber being either continuously connected to the external supply or periodic recharging thereof during pump operation.

It is the object of my invention to improve upon such prior arrangement by incorporating an air pumping chamber and piston within the assembly to automatically charge the damping or compression chamber with air from the atmosphere during operation of the fuel injection pump on the engine.

Following is a description of a preferred embodiment illustrating the principles of the invention, having reference to the drawing, wherein:

FIGURE 1 is a longitudinal sectional view through a unit fuel injector pump constructed in accordance with the invention.

FIGURE 2 is a sectional view taken substantially along the line 22 of FIGURE 1, showing the connection of the compression piston to the fuel pumping plunger.

Referring now to the drawing in detail, a unit fuel injector pump is illustrated having a body 1 to which liquid fuel is supplied under pressure at a fitting 2 and is conducted through an internal passage 3 to a reservoir chamber 4 formed in the lower extension or nut 5 threadedly secured to the lower end of the body. When the unit is installed on an engine, the nut 5 extends through a suitable opening in the cylinder head or other wall portion thereof (not shown) so as to locate its fuel discharge nozzle 6 within the engine combustion space. Suitably supported within the nut and surrounded by the annular reservoir 4- is a bushing 7 which forms the pumping cylinder for a plunger 8 reciprocably slidable therein. It will be understood that the fuel within the reservoir 4 is under relatively low pressure, in the order of 30 to 40 p.s.i., supplied at the fitting 2. Also as is conventional with such fuel injection pumps, provision may be made through additional passages and a second external fitting, not shown but similar to 3 and 2, respectively, for returning excess fuel to the tank or other supply source from the reservoir 4. Fuel inlet and bypass ports 9 and 10 extend through the side of the bushing 7 and are controlled by the plunger "so as to admit fuel at supply pressure to the space 12 within the bushing below the plunger, for delivery at high pressure, in the order of 2,000 to 20,000 p.s.i., to the nozzle 6 via the fuel outlet 11 on each downward or pumping stroke of the plunger.

The plunger 8 in also provided with bypass means to cooperate with the ports 9 and 10 in controlling the start and end of fuel injection during each such downward stroke of the plunger from its position shown. This by pass means includes an external metering groove 13 encircling the plunger at a distance from its lower end, together with transversely and axially drilled passages 14 and 15 which continuously connect the metering groove with the fuel pressure space 12 and outlet 11. The fuel inlet and bypass ports 9 and 10 are located in relation to the groove 13 and the lower end of the plunger such that during each pumping stroke of the plunger it first closes ofi port 10, then closes off port 9 (as groove 13 moves out of registry therewith), and thereafter reopens port 10 (as groove 13 moves into registry therewith) to relieve the high fuel pressure in the chamber 12 and thereby terminate the injection. The usual normally closed injection valve, illustrated as a spring biased poppet valve 16, is located in the fuel passage leading from the outlet 11 to the spray orifices 1.7 in the lower end of the nozzle.

The body 1 is provided with a series of connecting stepped bores 13, 19 and 20, of respectively increasing diameter, as shown, Bushing 7 has its upper end extending into and laterally supported within the bore 18. An external flange 21 on the bushing abuts the lower end of the body adjacent the bore 18, being held thereagainst by the nut 5 in which the lower end of the bushing is seated. As shown, the plunger extends upwardly through the bushing 7 and bore 18 of the body, through the bore 19 thereof, and into the bore 20. At the juncture of the bores 18 and 19 is a shoulder 22 on which is seated at lower spring retainer 23. Clamped to the body by the retainer 23, under the force of a plunger return spring 24, is a suitable gasket 25 to seal against air and fuel leakage between the bores 18 and 19. Sealably and slidably fitting the bores 19 and 20 are a compression piston 26 and a pumping piston 27, respectively. As shown, these pistons are of single unitary or integral construction, with the portion thereof forming the compression piston 26 having a hollow skirt 28 into which the upper end 29 of the plunger extends. A necked section 30 of the plunger, immediately below its upper end 29, is interengaged with a laterally open slot 31 in the upper end of this skirt to effect a connection of the plunger to the pistons 26, 27. Seated in the piston skirt 28 is a retainer washer 32 which thrustably supports the upper end of the spring 24.

A compression chamber 33 is thus formed by the bore 19 between the shoulder 22 and the compression piston 26, and the bore 20 forms a pumping chamber 34 between the pumping piston 27 and the shoulder 35 separating the bores 19 and 20. Passage means for the introduction of atmospheric air from the exterior of the pump body to the pumping chamber 34, and for delivery therefrom into the compression chamber 33, are provided in the pistons 26 and 27. The upper end of the pumping piston 27, which extends outwardly of the bore 20 for engagement with the pump driving member (not shown), is formed with a recess 36 in which a two-part valve body 37, 38 is seated. These two parts are provided with respective drilled and counterbored passages 39 and 40 which interconnect as shown to form a valve chamber 41. Opening inwardly of this valve chamber is a check valve 42, and opening outwardly thereof is a check valve 43. The

inwardly opening check valve 42 accommodates flow through the passage 39 into the valve chamber 41, from whence it may pass into the pumping chamber 34 through connecting passages 44 and 45. The check valve 43, in turn, accommodates flow into the compression chamber 33 via a drilled passage 46 from the valve chamber 41.

Although the compression chamber 33 is defined by the smaller of the two bores 19 and 20, it is of sufficient length that the volume ratio of this chamber exceeds that of the pumping chamber 34. As a result, the compression ratio of the pumping chamber exceeds that of the compression chamber, so that pressure developed in the former during each pumping stroke of the plunger always equals or exceeds the fluid pressure existing in the compression chamber 33. During operation, therefore, a substantial pressure is quickly built up within the compression chamber 33 after only a relatively few strokes, following which a state of balance between the two chambers 33 and 34 prevails, and thereafter the pumping chamber transfers only sufficient air to the compression chamber to compensate for leakage losses.

The air pressure which thus exists in the two chambers 33 and 34 serves to supplement the biasing force of the plunger return spring 24, and to damp any tendency of this spring to surge as the result of sudden decrease in fuel pressure in the space 12 below the plunger 8 when the plunger groove 13 uncovers the lower bushing port 10. Avoidance of such spring surging difliculties is facilitated by the fact that such complementary biasing force provided by the air compression and pumping action enables the spring 24 to have a relatively low load-deflection rate, with its inherent lower natural frequency of vibration.

By reason of my improved fuel injection pump incorporating its own air pump to charge the compression chamber 33, adequate damping force is assured automatically during operation, without need for any external source of supply for the damping fluid. It is appreciated that various changes in minor details of the parts will readily suggest themselves to others skilled in the art, without departing from the spirit and scope of the invention as hereinafter claimed.

I claim:

1. In a fuel injection pump having a plunger drivable on its pumping stroke to build up fuel pressure in a pumping cylinder sufiiciently to open an injection valve accommodating displacement of said fuel from the cylinder, and wherein said cylinder and plunger have means cooperating after the plunger has completed a predetermined portion of its said pumping stroke to relieve said built-up fuel pressure and thereby terminate said displacement, the combination therewith of a compression chamber, a compression piston operatively connected to said plunger for movement inwardly of said compression chamber on its compression stroke with movement of said plunger on its pumping stroke, an expansible fluid pump operable to deliver expansible fluid to said compression chamber including a pumping chamber of greater compression ratio than said compression chamber and a pumping piston operatively connected to said plunger for movement inwardly of said pumping chamber on its pumping stroke with movement of said plunger on its pumping stroke, and one-way passage means connecting said pumping chamber to said compression chamber for delivery of expansible fluid to the compression chamber by said expansible fluid pump during the pumping stroke of said pumping piston.

2. The invention of claim 1, wherein said pump comprises a body having aligned stepped bores including a first bore embracing and supporting said pumping cylinder, at second bore of larger diameter defining said compression chamber and a third bore of still larger diameter defining said pumping chamber bore, a shoulder at the juncture of said first and second bores, and a spring thrustably interposed between said shoulder and said compression piston for supplementing the expansible fluid pressure forces developed in said chambers during the pumping stroke of the plunger in effecting the return stroke of the plunger.

3. The invention of claim 1, wherein said compression and pumping pistons are integrally connected in adjacent endwise relation to each other, with the compression piston having a hollow skirt portion extending coaxially of said plunger, said plunger extending into said skirt portion and having a connection therein to said pistons, and including a plunger return spring encircling said plunger Within said skirt portion and thrustably interposed between said pumping cylinder and said connection.

4. The invention of claim 3 wherein said pumping piston has a portion extending outwardly of the pump from said pumping chamber for engagement with a pump driving member.

5. The invention of claim 4, wherein said one-way passage means comprises passages in said pumping and compression pistons for flow of said expansible fluid into said pumping chamber from the exterior of the pump and for flow of said fluid from the pumping chamber to said compression chamber, a valve chamber interconnecting said passages, and check valve means in said valve chamber blocking reverse flow through said passages.

References Cited by the Examiner UNITED STATES PATENTS 1,378,281 5/21 Ross 267-34 2,011,165 8/35 Steiner. 2,011,166 8/35 Steiner. 2,138,849 12/38 Gambrell 123139 2,342,003 2/44 Meyer 12390 2,569,233 9/51 Dickson et a1. 239533 3,006,556 10/61 Shade et al. 23988 FOREIGN PATENTS 105,944 3 27 Austria.

LAURENCE V. EFNER, Primary Examiner. RICHARD B. WILKINSON, Examiner. 

1. IN A FUEL INJECTION PUMP HAVING A PLUNGER DRIVABLE ON ITS PUMPING STROKE TO BUILD UP FUEL PRESSURE IN A PUMPING CYLINDER SUFFICIENTLY TO OPEN AN INJECTION VALVE ACCOMMODATING DISPLACEMENT OF SAID FUEL FROM THE CYLINDER, AND WHEREIN SAID CYLINDER AND PLUNGER HAVE MEANS COOPERATING AFTER THE PLUNGER HAS COMPLETED A PREDETERMINED PORTION OF ITS SAID PUMPING STROKE TO RELIEVE SAID BUILT-UP FUEL PRESSURE AND THEREBY TERMINATE SAID DISPLACEMENT, THE COMBINATION THEREWITH OF A COMPRESSION CHAMBER, A COMPRESSION PISTON OPERATIVELY CONNECTED TO SAID PLUNGER FOR MOVEMENT INWARDLY OF SAID COMPRESSION CHAMBER ON ITS COMPRESSION STROKE WITH MOVEMENT OF SAID PLUNGER ON ITS PUMPING STROKE, AN EXPANSIBLE FLUID PUMP OPERABLE TO DELIVER EXPANSIBLE FLUID TO SAID COMPRESSION CHAMBER INCLUDING A PUMPING CHAMBER OF GREATER COMPRESSION RATIO THAN SAID COMPRESSION CHAMBER AND A PUMPING PISTON OPERATIVELY CONNECTED TO SAID PLUNGER AND A PUMPING PISTON OPERATIVELY PUMPING CHAMBER ON ITS PUMPING STROKE WITH MOVEMENT OF SAID PLUNGER ON ITS PUMPING STROKE, ONE-WAY PASSAGE MEANS CONNECTING SAID PUMPING CHAMBER TO SAID COMPRESSION CHAMBER FOR DELIVERY OF EXPANSIBLE FLUID TO THE COMPRESSION CHAMBER BY SAID EXPANSIBLE FLUID PUMP DURING THE PUMPING STROKE OF SAID PUMPING PISTON. 